1. Filed of the Invention
This invention relates to an aluminum nitride sintered body and a process for its production. More specifically, it relates to an aluminum nitride sintered body which has high heat conductivity and is suitable as an electronic component part material such as a radiating substrate, and can be fired simultaneously with a conductor material, and to a process for its production.
2. Description of the Prior Art
In recent years, with higher performances and speeds of information processing devices, there has rapidly been a tendency to higher densities and higher integration of semiconductor integrated circuits constituting these devices, and consequently, semiconductor integrated circuit elements have undergone an increased electric power and the amounts of heat which these elements generate markedly increase. Accordingly, to operate the semiconductor integrated circuit normally and stably, the important problem is to remove the generated heat efficiently.
Since semiconductor packages having a conventional alumina substrate have low heat conductivity and radiation is insufficient, a beryllium oxide sintered body was proposed as a ceramic material having high heat conductivity. This material, however, encounters difficulty in use because of its toxicity.
Hence, an attention has been paid to an aluminum nitride sintered body which has various excellent properties, for example, a high mechanical strength at room temperature to a high temperature, high electrical insulation, high heat-conductivity and a coefficient of thermal expansion close to that of a single crystal of silicon as a highly heat conducting substrate material superseding the beryllium oxide sintered body.
Intrinsically, however, aluminum nitride is difficult to sinter, and it is difficult to obtain a high density sintered body having high heat conductivity from aluminum nitride alone. Accordingly, it has been the previous practice to add compounds of elements of Group IIa or IIIa of the periodic table, for example, alkaline earth metals such as calcium, strontium and barium, or compounds of yttrium and rare earth elements as sintering aids to give sintered bodies of high density.
For example, U.S. Pat. No. 4,746,437 discloses that a mixture of an aluminum nitride powder, a compound of a metal of group IIa of the periodic table such as calcium, strontium or barium, and a compound of a metal of group IIIa of the periodic table typified by yttrium is fired. Since the resulting sintered body has insufficient flexural strength, it is susceptible to breakage or cracking during handling. Furthermore, when it is fired simultaneously with a conductor material constituting a wiring at the time of preparing a substrate board, its adhesion strength is insufficient.
U.S. patent application No. 386,789 to the present inventors discloses that by firing a molded article of a composition composed of aluminum nitride, a compound represented by Yb.sub.b O.sub.3 or Er.sub.2 O.sub.3 and a component represented by CaO as oxides, the intergranular phase in the sintered body is removed by volatilization, and aluminum nitride sintered body having increased heat conductivity is produced. This method, however requires firing at high temperatures to volatilize the intergranular phase, and poor fired bodies are formed because the surface of the sintered body is roughened or warpage occurs. Furthermore, the mechanical strength of the sintered body is not entirely satisfactory.